As the US’s network of solar panels, wind turbines and geothermal grows ever bigger, these scientists are growing increasingly worried about the stress such 21st century power sources could place on a grid designed for the 20th century, the paper reports.

It all boils down to green energy’s inherent unpredictability. Despite weather predictions, no one can say for sure when the wind will blow or the sun will shine. As such, high winds, for example – even if forecast – can lead to a spike in energy at an inopportune moment.

The role of the grid is to keep supply steady and stable. This task includes calculating how much energy to pump into the system to meet demand but not to overload the grid. An unexpected spike can crash the system.

A recent Caltech report predicted that by 2030, about $1 trillion will have been spent in the US bringing the grid up to date, the paper reports.

California – a state that has been at the forefront of renewables adoption – has taken some of the earliest steps to mitigate the problems. The California Public Utilities Commission has recently ordered large power companies to invest in developing storage technologies to “bottle up” wind and solar power, allowing the energy to be released strategically overtime.

Such is the problem that some systems operators are considering paying people to not produce power, the paper reports.

One of the paper mill’s biggest consumers of energy is its pulping machine. The Port Angeles, Wash., plant generally runs this machine at its most energy-efficient, rather than its fastest, speed, meaning that their is regularly the potential to use more energy and pulp paper at a faster rate – a win-win situation for BPA and Nippon.